Lag all of the suden

[ikica1996]

I5 2500k 3,3-3,7ghz turbo (with coolermaster hyper 212+ can achive over 4,5 stable)
MSI GTX560Ti Hawk can oc to 1ghz
4GB DDR3 Kingston Hyper X
MSI P67-C43 (B3) (kinda cheap but does its job nice and can overclock like a mf)
Thermaltake Toughpower XT 775
WD Caviar Black Sata 3 1TB 7200rp

So i built this system myself and im really proud of it, it can max out any game 1080p 60fps stable but all of the suden i have noticed that some games lag a bit not to much but lag like games that i could play 60fps or more are now 40-50 and i havent changed anything the only thing i can think off is that one time i forgot to set the cooler profile on my gfx and the memory temps were 100 C for about 3-5min and thats when it all started i think so before i take my pc for repairs i wanted to ask the community for opinions also i dont know if its important or not but my cpu cable was a little bit disconnected for about a month and it caused the pc to shut down sometimes could it also be that that damaged some part ? (for anyone that says you cant run battlefield 3 or metro 2033 all max with AA on 1080p i have and it worked great battlefield 3 and metro 2033 60+ fps) sry for the long post thanks in advance

 

[HEXiT]

something as basic as a bad reg entry can cause games to lag. if the pc kept shutting down this is 1 of the first places i would look. run ccleaner's reg cleaner multiple times till you have no errors. clean out any old files and make sure you have at least 15% hdd space free. not doing so will affect system performance.
check your hdd for fragmentation you may want to run chkdsk just to be sure you havent created any soft errors when the pc was randomly shutting off.
if you pc is still lagging try disabling your av while you play a game to see if that changes anything. (some av's can suddenly become a pain when they get updates to new versions) so its worth checking just to take off the list.
use hw monitor to measure the volts, temps and usage of your cpu/gpu and motherboard. use gpu-z and check on the vddc temps and volts to make sure there within spec. real temp to check temps of the cpu...
stress test everything. with prime 95 and fur mark. they will send your components to the max temps your oc will induce ever. if there both stable then you can pretty much discount stability and temps being the issue.
check your ram by running hyper pi. run the 32m test if your pc locks up its likely your ram is unstable.
really there is so much that could have gone wrong your gonna have to do a full diagnostic run.
but b4 you do anything. open the case and make sure everything is connected and seated properly... the leads should be tight enough so they cant work loose so i have no idea how you managed to have a cpu power lead disconnect. most of the time i have to fight to get mine to disconnect from the motherboard...

but yeah start with the reg clean and defrag first then do the rest if they dont deliver results.